import {
  LinearFilter,
  LinearMipmapLinearFilter,
  LinearMipmapNearestFilter,
  NearestFilter,
  NearestMipmapLinearFilter,
  NearestMipmapNearestFilter,
  RGBFormat,
  RGBAFormat,
  DepthFormat,
  DepthStencilFormat,
  UnsignedShortType,
  UnsignedIntType,
  UnsignedInt248Type,
  FloatType,
  HalfFloatType,
  MirroredRepeatWrapping,
  ClampToEdgeWrapping,
  RepeatWrapping
} from '../../constants.js';
import {MathUtils} from '../../math/MathUtils.js';

function WebGLTextures(_gl, extensions, state, properties, capabilities, utils, info) {

  const isWebGL2 = capabilities.isWebGL2;
  const maxTextures = capabilities.maxTextures;
  const maxCubemapSize = capabilities.maxCubemapSize;
  const maxTextureSize = capabilities.maxTextureSize;
  const maxSamples = capabilities.maxSamples;

  const _videoTextures = new WeakMap();
  let _canvas;

  // cordova iOS (as of 5.0) still uses UIWebView, which provides OffscreenCanvas,
  // also OffscreenCanvas.getContext("webgl"), but not OffscreenCanvas.getContext("2d")!
  // Some implementations may only implement OffscreenCanvas partially (e.g. lacking 2d).

  let useOffscreenCanvas = false;

  try {

    useOffscreenCanvas = typeof OffscreenCanvas !== 'undefined'
      && (new OffscreenCanvas(1, 1).getContext("2d")) !== null;

  } catch (err) {

    // Ignore any errors

  }

  function createCanvas(width, height) {

    // Use OffscreenCanvas when available. Specially needed in web workers

    return useOffscreenCanvas ?
      new OffscreenCanvas(width, height) :
      document.createElementNS('http://www.w3.org/1999/xhtml', 'canvas');

  }

  function resizeImage(image, needsPowerOfTwo, needsNewCanvas, maxSize) {

    let scale = 1;

    // handle case if texture exceeds max size

    if (image.width > maxSize || image.height > maxSize) {

      scale = maxSize / Math.max(image.width, image.height);

    }

    // only perform resize if necessary

    if (scale < 1 || needsPowerOfTwo === true) {

      // only perform resize for certain image types

      if ((typeof HTMLImageElement !== 'undefined' && image instanceof HTMLImageElement) ||
        (typeof HTMLCanvasElement !== 'undefined' && image instanceof HTMLCanvasElement) ||
        (typeof ImageBitmap !== 'undefined' && image instanceof ImageBitmap)) {

        const floor = needsPowerOfTwo ? MathUtils.floorPowerOfTwo : Math.floor;

        const width = floor(scale * image.width);
        const height = floor(scale * image.height);

        if (_canvas === undefined) _canvas = createCanvas(width, height);

        // cube textures can't reuse the same canvas

        const canvas = needsNewCanvas ? createCanvas(width, height) : _canvas;

        canvas.width = width;
        canvas.height = height;

        const context = canvas.getContext('2d');
        context.drawImage(image, 0, 0, width, height);

        console.warn('THREE.WebGLRenderer: Texture has been resized from (' + image.width + 'x' + image.height + ') to (' + width + 'x' + height + ').');

        return canvas;

      } else {

        if ('data' in image) {

          console.warn('THREE.WebGLRenderer: Image in DataTexture is too big (' + image.width + 'x' + image.height + ').');

        }

        return image;

      }

    }

    return image;

  }

  function isPowerOfTwo(image) {

    return MathUtils.isPowerOfTwo(image.width) && MathUtils.isPowerOfTwo(image.height);

  }

  function textureNeedsPowerOfTwo(texture) {

    if (isWebGL2) return false;

    return (texture.wrapS !== ClampToEdgeWrapping || texture.wrapT !== ClampToEdgeWrapping) ||
      (texture.minFilter !== NearestFilter && texture.minFilter !== LinearFilter);

  }

  function textureNeedsGenerateMipmaps(texture, supportsMips) {

    return texture.generateMipmaps && supportsMips &&
      texture.minFilter !== NearestFilter && texture.minFilter !== LinearFilter;

  }

  function generateMipmap(target, texture, width, height) {

    _gl.generateMipmap(target);

    const textureProperties = properties.get(texture);

    // Note: Math.log( x ) * Math.LOG2E used instead of Math.log2( x ) which is not supported by IE11
    textureProperties.__maxMipLevel = Math.log(Math.max(width, height)) * Math.LOG2E;

  }

  function getInternalFormat(internalFormatName, glFormat, glType) {

    if (isWebGL2 === false) return glFormat;

    if (internalFormatName !== null) {

      if (_gl[internalFormatName] !== undefined) return _gl[internalFormatName];

      console.warn('THREE.WebGLRenderer: Attempt to use non-existing WebGL internal format \'' + internalFormatName + '\'');

    }

    let internalFormat = glFormat;

    if (glFormat === _gl.RED) {

      if (glType === _gl.FLOAT) internalFormat = _gl.R32F;
      if (glType === _gl.HALF_FLOAT) internalFormat = _gl.R16F;
      if (glType === _gl.UNSIGNED_BYTE) internalFormat = _gl.R8;

    }

    if (glFormat === _gl.RGB) {

      if (glType === _gl.FLOAT) internalFormat = _gl.RGB32F;
      if (glType === _gl.HALF_FLOAT) internalFormat = _gl.RGB16F;
      if (glType === _gl.UNSIGNED_BYTE) internalFormat = _gl.RGB8;

    }

    if (glFormat === _gl.RGBA) {

      if (glType === _gl.FLOAT) internalFormat = _gl.RGBA32F;
      if (glType === _gl.HALF_FLOAT) internalFormat = _gl.RGBA16F;
      if (glType === _gl.UNSIGNED_BYTE) internalFormat = _gl.RGBA8;

    }

    if (internalFormat === _gl.R16F || internalFormat === _gl.R32F ||
      internalFormat === _gl.RGBA16F || internalFormat === _gl.RGBA32F) {

      extensions.get('EXT_color_buffer_float');

    }

    return internalFormat;

  }

  // Fallback filters for non-power-of-2 textures

  function filterFallback(f) {

    if (f === NearestFilter || f === NearestMipmapNearestFilter || f === NearestMipmapLinearFilter) {

      return _gl.NEAREST;

    }

    return _gl.LINEAR;

  }

  //

  function onTextureDispose(event) {

    const texture = event.target;

    texture.removeEventListener('dispose', onTextureDispose);

    deallocateTexture(texture);

    if (texture.isVideoTexture) {

      _videoTextures.delete(texture);

    }

    info.memory.textures--;

  }

  function onRenderTargetDispose(event) {

    const renderTarget = event.target;

    renderTarget.removeEventListener('dispose', onRenderTargetDispose);

    deallocateRenderTarget(renderTarget);

    info.memory.textures--;

  }

  //

  function deallocateTexture(texture) {

    const textureProperties = properties.get(texture);

    if (textureProperties.__webglInit === undefined) return;

    _gl.deleteTexture(textureProperties.__webglTexture);

    properties.remove(texture);

  }

  function deallocateRenderTarget(renderTarget) {

    const renderTargetProperties = properties.get(renderTarget);
    const textureProperties = properties.get(renderTarget.texture);

    if (!renderTarget) return;

    if (textureProperties.__webglTexture !== undefined) {

      _gl.deleteTexture(textureProperties.__webglTexture);

    }

    if (renderTarget.depthTexture) {

      renderTarget.depthTexture.dispose();

    }

    if (renderTarget.isWebGLCubeRenderTarget) {

      for (let i = 0; i < 6; i++) {

        _gl.deleteFramebuffer(renderTargetProperties.__webglFramebuffer[i]);
        if (renderTargetProperties.__webglDepthbuffer) _gl.deleteRenderbuffer(renderTargetProperties.__webglDepthbuffer[i]);

      }

    } else {

      _gl.deleteFramebuffer(renderTargetProperties.__webglFramebuffer);
      if (renderTargetProperties.__webglDepthbuffer) _gl.deleteRenderbuffer(renderTargetProperties.__webglDepthbuffer);
      if (renderTargetProperties.__webglMultisampledFramebuffer) _gl.deleteFramebuffer(renderTargetProperties.__webglMultisampledFramebuffer);
      if (renderTargetProperties.__webglColorRenderbuffer) _gl.deleteRenderbuffer(renderTargetProperties.__webglColorRenderbuffer);
      if (renderTargetProperties.__webglDepthRenderbuffer) _gl.deleteRenderbuffer(renderTargetProperties.__webglDepthRenderbuffer);

    }

    properties.remove(renderTarget.texture);
    properties.remove(renderTarget);

  }

  //

  let textureUnits = 0;

  function resetTextureUnits() {

    textureUnits = 0;

  }

  function allocateTextureUnit() {

    const textureUnit = textureUnits;

    if (textureUnit >= maxTextures) {

      console.warn('THREE.WebGLTextures: Trying to use ' + textureUnit + ' texture units while this GPU supports only ' + maxTextures);

    }

    textureUnits += 1;

    return textureUnit;

  }

  //

  function setTexture2D(texture, slot) {

    const textureProperties = properties.get(texture);

    if (texture.isVideoTexture) updateVideoTexture(texture);

    if (texture.version > 0 && textureProperties.__version !== texture.version) {

      const image = texture.image;

      if (image === undefined) {

        console.warn('THREE.WebGLRenderer: Texture marked for update but image is undefined');

      } else if (image.complete === false) {

        console.warn('THREE.WebGLRenderer: Texture marked for update but image is incomplete');

      } else {

        uploadTexture(textureProperties, texture, slot);
        return;

      }

    }

    state.activeTexture(_gl.TEXTURE0 + slot);
    state.bindTexture(_gl.TEXTURE_2D, textureProperties.__webglTexture);

  }

  function setTexture2DArray(texture, slot) {

    const textureProperties = properties.get(texture);

    if (texture.version > 0 && textureProperties.__version !== texture.version) {

      uploadTexture(textureProperties, texture, slot);
      return;

    }

    state.activeTexture(_gl.TEXTURE0 + slot);
    state.bindTexture(_gl.TEXTURE_2D_ARRAY, textureProperties.__webglTexture);

  }

  function setTexture3D(texture, slot) {

    const textureProperties = properties.get(texture);

    if (texture.version > 0 && textureProperties.__version !== texture.version) {

      uploadTexture(textureProperties, texture, slot);
      return;

    }

    state.activeTexture(_gl.TEXTURE0 + slot);
    state.bindTexture(_gl.TEXTURE_3D, textureProperties.__webglTexture);

  }

  function setTextureCube(texture, slot) {

    if (texture.image.length !== 6) return;

    const textureProperties = properties.get(texture);

    if (texture.version > 0 && textureProperties.__version !== texture.version) {

      initTexture(textureProperties, texture);

      state.activeTexture(_gl.TEXTURE0 + slot);
      state.bindTexture(_gl.TEXTURE_CUBE_MAP, textureProperties.__webglTexture);

      _gl.pixelStorei(_gl.UNPACK_FLIP_Y_WEBGL, texture.flipY);

      const isCompressed = (texture && (texture.isCompressedTexture || texture.image[0].isCompressedTexture));
      const isDataTexture = (texture.image[0] && texture.image[0].isDataTexture);

      const cubeImage = [];

      for (let i = 0; i < 6; i++) {

        if (!isCompressed && !isDataTexture) {

          cubeImage[i] = resizeImage(texture.image[i], false, true, maxCubemapSize);

        } else {

          cubeImage[i] = isDataTexture ? texture.image[i].image : texture.image[i];

        }

      }

      const image = cubeImage[0],
        supportsMips = isPowerOfTwo(image) || isWebGL2,
        glFormat = utils.convert(texture.format),
        glType = utils.convert(texture.type),
        glInternalFormat = getInternalFormat(texture.internalFormat, glFormat, glType);

      setTextureParameters(_gl.TEXTURE_CUBE_MAP, texture, supportsMips);

      let mipmaps;

      if (isCompressed) {

        for (let i = 0; i < 6; i++) {

          mipmaps = cubeImage[i].mipmaps;

          for (let j = 0; j < mipmaps.length; j++) {

            const mipmap = mipmaps[j];

            if (texture.format !== RGBAFormat && texture.format !== RGBFormat) {

              if (glFormat !== null) {

                state.compressedTexImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, j, glInternalFormat, mipmap.width, mipmap.height, 0, mipmap.data);

              } else {

                console.warn('THREE.WebGLRenderer: Attempt to load unsupported compressed texture format in .setTextureCube()');

              }

            } else {

              state.texImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, j, glInternalFormat, mipmap.width, mipmap.height, 0, glFormat, glType, mipmap.data);

            }

          }

        }

        textureProperties.__maxMipLevel = mipmaps.length - 1;

      } else {

        mipmaps = texture.mipmaps;

        for (let i = 0; i < 6; i++) {

          if (isDataTexture) {

            state.texImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, glInternalFormat, cubeImage[i].width, cubeImage[i].height, 0, glFormat, glType, cubeImage[i].data);

            for (let j = 0; j < mipmaps.length; j++) {

              const mipmap = mipmaps[j];
              const mipmapImage = mipmap.image[i].image;

              state.texImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, j + 1, glInternalFormat, mipmapImage.width, mipmapImage.height, 0, glFormat, glType, mipmapImage.data);

            }

          } else {

            state.texImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, glInternalFormat, glFormat, glType, cubeImage[i]);

            for (let j = 0; j < mipmaps.length; j++) {

              const mipmap = mipmaps[j];

              state.texImage2D(_gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, j + 1, glInternalFormat, glFormat, glType, mipmap.image[i]);

            }

          }

        }

        textureProperties.__maxMipLevel = mipmaps.length;

      }

      if (textureNeedsGenerateMipmaps(texture, supportsMips)) {

        // We assume images for cube map have the same size.
        generateMipmap(_gl.TEXTURE_CUBE_MAP, texture, image.width, image.height);

      }

      textureProperties.__version = texture.version;

      if (texture.onUpdate) texture.onUpdate(texture);

    } else {

      state.activeTexture(_gl.TEXTURE0 + slot);
      state.bindTexture(_gl.TEXTURE_CUBE_MAP, textureProperties.__webglTexture);

    }

  }

  function setTextureCubeDynamic(texture, slot) {

    state.activeTexture(_gl.TEXTURE0 + slot);
    state.bindTexture(_gl.TEXTURE_CUBE_MAP, properties.get(texture).__webglTexture);

  }

  const wrappingToGL = {
    [RepeatWrapping]: _gl.REPEAT,
    [ClampToEdgeWrapping]: _gl.CLAMP_TO_EDGE,
    [MirroredRepeatWrapping]: _gl.MIRRORED_REPEAT
  };

  const filterToGL = {
    [NearestFilter]: _gl.NEAREST,
    [NearestMipmapNearestFilter]: _gl.NEAREST_MIPMAP_NEAREST,
    [NearestMipmapLinearFilter]: _gl.NEAREST_MIPMAP_LINEAR,

    [LinearFilter]: _gl.LINEAR,
    [LinearMipmapNearestFilter]: _gl.LINEAR_MIPMAP_NEAREST,
    [LinearMipmapLinearFilter]: _gl.LINEAR_MIPMAP_LINEAR
  };

  function setTextureParameters(textureType, texture, supportsMips) {

    if (supportsMips) {

      _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_S, wrappingToGL[texture.wrapS]);
      _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_T, wrappingToGL[texture.wrapT]);

      if (textureType === _gl.TEXTURE_3D || textureType === _gl.TEXTURE_2D_ARRAY) {

        _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_R, wrappingToGL[texture.wrapR]);

      }

      _gl.texParameteri(textureType, _gl.TEXTURE_MAG_FILTER, filterToGL[texture.magFilter]);
      _gl.texParameteri(textureType, _gl.TEXTURE_MIN_FILTER, filterToGL[texture.minFilter]);

    } else {

      _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_S, _gl.CLAMP_TO_EDGE);
      _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_T, _gl.CLAMP_TO_EDGE);

      if (textureType === _gl.TEXTURE_3D || textureType === _gl.TEXTURE_2D_ARRAY) {

        _gl.texParameteri(textureType, _gl.TEXTURE_WRAP_R, _gl.CLAMP_TO_EDGE);

      }

      if (texture.wrapS !== ClampToEdgeWrapping || texture.wrapT !== ClampToEdgeWrapping) {

        console.warn('THREE.WebGLRenderer: Texture is not power of two. Texture.wrapS and Texture.wrapT should be set to THREE.ClampToEdgeWrapping.');

      }

      _gl.texParameteri(textureType, _gl.TEXTURE_MAG_FILTER, filterFallback(texture.magFilter));
      _gl.texParameteri(textureType, _gl.TEXTURE_MIN_FILTER, filterFallback(texture.minFilter));

      if (texture.minFilter !== NearestFilter && texture.minFilter !== LinearFilter) {

        console.warn('THREE.WebGLRenderer: Texture is not power of two. Texture.minFilter should be set to THREE.NearestFilter or THREE.LinearFilter.');

      }

    }

    const extension = extensions.get('EXT_texture_filter_anisotropic');

    if (extension) {

      if (texture.type === FloatType && extensions.get('OES_texture_float_linear') === null) return;
      if (texture.type === HalfFloatType && (isWebGL2 || extensions.get('OES_texture_half_float_linear')) === null) return;

      if (texture.anisotropy > 1 || properties.get(texture).__currentAnisotropy) {

        _gl.texParameterf(textureType, extension.TEXTURE_MAX_ANISOTROPY_EXT, Math.min(texture.anisotropy, capabilities.getMaxAnisotropy()));
        properties.get(texture).__currentAnisotropy = texture.anisotropy;

      }

    }

  }

  function initTexture(textureProperties, texture) {

    if (textureProperties.__webglInit === undefined) {

      textureProperties.__webglInit = true;

      texture.addEventListener('dispose', onTextureDispose);

      textureProperties.__webglTexture = _gl.createTexture();

      info.memory.textures++;

    }

  }

  function uploadTexture(textureProperties, texture, slot) {

    let textureType = _gl.TEXTURE_2D;

    if (texture.isDataTexture2DArray) textureType = _gl.TEXTURE_2D_ARRAY;
    if (texture.isDataTexture3D) textureType = _gl.TEXTURE_3D;

    initTexture(textureProperties, texture);

    state.activeTexture(_gl.TEXTURE0 + slot);
    state.bindTexture(textureType, textureProperties.__webglTexture);

    _gl.pixelStorei(_gl.UNPACK_FLIP_Y_WEBGL, texture.flipY);
    _gl.pixelStorei(_gl.UNPACK_PREMULTIPLY_ALPHA_WEBGL, texture.premultiplyAlpha);
    _gl.pixelStorei(_gl.UNPACK_ALIGNMENT, texture.unpackAlignment);

    const needsPowerOfTwo = textureNeedsPowerOfTwo(texture) && isPowerOfTwo(texture.image) === false;
    const image = resizeImage(texture.image, needsPowerOfTwo, false, maxTextureSize);

    const supportsMips = isPowerOfTwo(image) || isWebGL2,
      glFormat = utils.convert(texture.format);

    let glType = utils.convert(texture.type),
      glInternalFormat = getInternalFormat(texture.internalFormat, glFormat, glType);

    setTextureParameters(textureType, texture, supportsMips);

    let mipmap;
    const mipmaps = texture.mipmaps;

    if (texture.isDepthTexture) {

      // populate depth texture with dummy data

      glInternalFormat = _gl.DEPTH_COMPONENT;

      if (isWebGL2) {

        if (texture.type === FloatType) {

          glInternalFormat = _gl.DEPTH_COMPONENT32F;

        } else if (texture.type === UnsignedIntType) {

          glInternalFormat = _gl.DEPTH_COMPONENT24;

        } else if (texture.type === UnsignedInt248Type) {

          glInternalFormat = _gl.DEPTH24_STENCIL8;

        } else {

          glInternalFormat = _gl.DEPTH_COMPONENT16; // WebGL2 requires sized internalformat for glTexImage2D

        }

      } else {

        if (texture.type === FloatType) {

          console.error('WebGLRenderer: Floating point depth texture requires WebGL2.');

        }

      }

      // validation checks for WebGL 1

      if (texture.format === DepthFormat && glInternalFormat === _gl.DEPTH_COMPONENT) {

        // The error INVALID_OPERATION is generated by texImage2D if format and internalformat are
        // DEPTH_COMPONENT and type is not UNSIGNED_SHORT or UNSIGNED_INT
        // (https://www.khronos.org/registry/webgl/extensions/WEBGL_depth_texture/)
        if (texture.type !== UnsignedShortType && texture.type !== UnsignedIntType) {

          console.warn('THREE.WebGLRenderer: Use UnsignedShortType or UnsignedIntType for DepthFormat DepthTexture.');

          texture.type = UnsignedShortType;
          glType = utils.convert(texture.type);

        }

      }

      if (texture.format === DepthStencilFormat && glInternalFormat === _gl.DEPTH_COMPONENT) {

        // Depth stencil textures need the DEPTH_STENCIL internal format
        // (https://www.khronos.org/registry/webgl/extensions/WEBGL_depth_texture/)
        glInternalFormat = _gl.DEPTH_STENCIL;

        // The error INVALID_OPERATION is generated by texImage2D if format and internalformat are
        // DEPTH_STENCIL and type is not UNSIGNED_INT_24_8_WEBGL.
        // (https://www.khronos.org/registry/webgl/extensions/WEBGL_depth_texture/)
        if (texture.type !== UnsignedInt248Type) {

          console.warn('THREE.WebGLRenderer: Use UnsignedInt248Type for DepthStencilFormat DepthTexture.');

          texture.type = UnsignedInt248Type;
          glType = utils.convert(texture.type);

        }

      }

      //

      state.texImage2D(_gl.TEXTURE_2D, 0, glInternalFormat, image.width, image.height, 0, glFormat, glType, null);

    } else if (texture.isDataTexture) {

      // use manually created mipmaps if available
      // if there are no manual mipmaps
      // set 0 level mipmap and then use GL to generate other mipmap levels

      if (mipmaps.length > 0 && supportsMips) {

        for (let i = 0, il = mipmaps.length; i < il; i++) {

          mipmap = mipmaps[i];
          state.texImage2D(_gl.TEXTURE_2D, i, glInternalFormat, mipmap.width, mipmap.height, 0, glFormat, glType, mipmap.data);

        }

        texture.generateMipmaps = false;
        textureProperties.__maxMipLevel = mipmaps.length - 1;

      } else {

        state.texImage2D(_gl.TEXTURE_2D, 0, glInternalFormat, image.width, image.height, 0, glFormat, glType, image.data);
        textureProperties.__maxMipLevel = 0;

      }

    } else if (texture.isCompressedTexture) {

      for (let i = 0, il = mipmaps.length; i < il; i++) {

        mipmap = mipmaps[i];

        if (texture.format !== RGBAFormat && texture.format !== RGBFormat) {

          if (glFormat !== null) {

            state.compressedTexImage2D(_gl.TEXTURE_2D, i, glInternalFormat, mipmap.width, mipmap.height, 0, mipmap.data);

          } else {

            console.warn('THREE.WebGLRenderer: Attempt to load unsupported compressed texture format in .uploadTexture()');

          }

        } else {

          state.texImage2D(_gl.TEXTURE_2D, i, glInternalFormat, mipmap.width, mipmap.height, 0, glFormat, glType, mipmap.data);

        }

      }

      textureProperties.__maxMipLevel = mipmaps.length - 1;

    } else if (texture.isDataTexture2DArray) {

      state.texImage3D(_gl.TEXTURE_2D_ARRAY, 0, glInternalFormat, image.width, image.height, image.depth, 0, glFormat, glType, image.data);
      textureProperties.__maxMipLevel = 0;

    } else if (texture.isDataTexture3D) {

      state.texImage3D(_gl.TEXTURE_3D, 0, glInternalFormat, image.width, image.height, image.depth, 0, glFormat, glType, image.data);
      textureProperties.__maxMipLevel = 0;

    } else {

      // regular Texture (image, video, canvas)

      // use manually created mipmaps if available
      // if there are no manual mipmaps
      // set 0 level mipmap and then use GL to generate other mipmap levels

      if (mipmaps.length > 0 && supportsMips) {

        for (let i = 0, il = mipmaps.length; i < il; i++) {

          mipmap = mipmaps[i];
          state.texImage2D(_gl.TEXTURE_2D, i, glInternalFormat, glFormat, glType, mipmap);

        }

        texture.generateMipmaps = false;
        textureProperties.__maxMipLevel = mipmaps.length - 1;

      } else {

        state.texImage2D(_gl.TEXTURE_2D, 0, glInternalFormat, glFormat, glType, image);
        textureProperties.__maxMipLevel = 0;

      }

    }

    if (textureNeedsGenerateMipmaps(texture, supportsMips)) {

      generateMipmap(textureType, texture, image.width, image.height);

    }

    textureProperties.__version = texture.version;

    if (texture.onUpdate) texture.onUpdate(texture);

  }

  // Render targets

  // Setup storage for target texture and bind it to correct framebuffer
  function setupFrameBufferTexture(framebuffer, renderTarget, attachment, textureTarget) {

    const glFormat = utils.convert(renderTarget.texture.format);
    const glType = utils.convert(renderTarget.texture.type);
    const glInternalFormat = getInternalFormat(renderTarget.texture.internalFormat, glFormat, glType);
    state.texImage2D(textureTarget, 0, glInternalFormat, renderTarget.width, renderTarget.height, 0, glFormat, glType, null);
    _gl.bindFramebuffer(_gl.FRAMEBUFFER, framebuffer);
    _gl.framebufferTexture2D(_gl.FRAMEBUFFER, attachment, textureTarget, properties.get(renderTarget.texture).__webglTexture, 0);
    _gl.bindFramebuffer(_gl.FRAMEBUFFER, null);

  }

  // Setup storage for internal depth/stencil buffers and bind to correct framebuffer
  function setupRenderBufferStorage(renderbuffer, renderTarget, isMultisample) {

    _gl.bindRenderbuffer(_gl.RENDERBUFFER, renderbuffer);

    if (renderTarget.depthBuffer && !renderTarget.stencilBuffer) {

      let glInternalFormat = _gl.DEPTH_COMPONENT16;

      if (isMultisample) {

        const depthTexture = renderTarget.depthTexture;

        if (depthTexture && depthTexture.isDepthTexture) {

          if (depthTexture.type === FloatType) {

            glInternalFormat = _gl.DEPTH_COMPONENT32F;

          } else if (depthTexture.type === UnsignedIntType) {

            glInternalFormat = _gl.DEPTH_COMPONENT24;

          }

        }

        const samples = getRenderTargetSamples(renderTarget);

        _gl.renderbufferStorageMultisample(_gl.RENDERBUFFER, samples, glInternalFormat, renderTarget.width, renderTarget.height);

      } else {

        _gl.renderbufferStorage(_gl.RENDERBUFFER, glInternalFormat, renderTarget.width, renderTarget.height);

      }

      _gl.framebufferRenderbuffer(_gl.FRAMEBUFFER, _gl.DEPTH_ATTACHMENT, _gl.RENDERBUFFER, renderbuffer);

    } else if (renderTarget.depthBuffer && renderTarget.stencilBuffer) {

      if (isMultisample) {

        const samples = getRenderTargetSamples(renderTarget);

        _gl.renderbufferStorageMultisample(_gl.RENDERBUFFER, samples, _gl.DEPTH24_STENCIL8, renderTarget.width, renderTarget.height);

      } else {

        _gl.renderbufferStorage(_gl.RENDERBUFFER, _gl.DEPTH_STENCIL, renderTarget.width, renderTarget.height);

      }


      _gl.framebufferRenderbuffer(_gl.FRAMEBUFFER, _gl.DEPTH_STENCIL_ATTACHMENT, _gl.RENDERBUFFER, renderbuffer);

    } else {

      const glFormat = utils.convert(renderTarget.texture.format);
      const glType = utils.convert(renderTarget.texture.type);
      const glInternalFormat = getInternalFormat(renderTarget.texture.internalFormat, glFormat, glType);

      if (isMultisample) {

        const samples = getRenderTargetSamples(renderTarget);

        _gl.renderbufferStorageMultisample(_gl.RENDERBUFFER, samples, glInternalFormat, renderTarget.width, renderTarget.height);

      } else {

        _gl.renderbufferStorage(_gl.RENDERBUFFER, glInternalFormat, renderTarget.width, renderTarget.height);

      }

    }

    _gl.bindRenderbuffer(_gl.RENDERBUFFER, null);

  }

  // Setup resources for a Depth Texture for a FBO (needs an extension)
  function setupDepthTexture(framebuffer, renderTarget) {

    const isCube = (renderTarget && renderTarget.isWebGLCubeRenderTarget);
    if (isCube) throw new Error('Depth Texture with cube render targets is not supported');

    _gl.bindFramebuffer(_gl.FRAMEBUFFER, framebuffer);

    if (!(renderTarget.depthTexture && renderTarget.depthTexture.isDepthTexture)) {

      throw new Error('renderTarget.depthTexture must be an instance of THREE.DepthTexture');

    }

    // upload an empty depth texture with framebuffer size
    if (!properties.get(renderTarget.depthTexture).__webglTexture ||
      renderTarget.depthTexture.image.width !== renderTarget.width ||
      renderTarget.depthTexture.image.height !== renderTarget.height) {

      renderTarget.depthTexture.image.width = renderTarget.width;
      renderTarget.depthTexture.image.height = renderTarget.height;
      renderTarget.depthTexture.needsUpdate = true;

    }

    setTexture2D(renderTarget.depthTexture, 0);

    const webglDepthTexture = properties.get(renderTarget.depthTexture).__webglTexture;

    if (renderTarget.depthTexture.format === DepthFormat) {

      _gl.framebufferTexture2D(_gl.FRAMEBUFFER, _gl.DEPTH_ATTACHMENT, _gl.TEXTURE_2D, webglDepthTexture, 0);

    } else if (renderTarget.depthTexture.format === DepthStencilFormat) {

      _gl.framebufferTexture2D(_gl.FRAMEBUFFER, _gl.DEPTH_STENCIL_ATTACHMENT, _gl.TEXTURE_2D, webglDepthTexture, 0);

    } else {

      throw new Error('Unknown depthTexture format');

    }

  }

  // Setup GL resources for a non-texture depth buffer
  function setupDepthRenderbuffer(renderTarget) {

    const renderTargetProperties = properties.get(renderTarget);

    const isCube = (renderTarget.isWebGLCubeRenderTarget === true);

    if (renderTarget.depthTexture) {

      if (isCube) throw new Error('target.depthTexture not supported in Cube render targets');

      setupDepthTexture(renderTargetProperties.__webglFramebuffer, renderTarget);

    } else {

      if (isCube) {

        renderTargetProperties.__webglDepthbuffer = [];

        for (let i = 0; i < 6; i++) {

          _gl.bindFramebuffer(_gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer[i]);
          renderTargetProperties.__webglDepthbuffer[i] = _gl.createRenderbuffer();
          setupRenderBufferStorage(renderTargetProperties.__webglDepthbuffer[i], renderTarget, false);

        }

      } else {

        _gl.bindFramebuffer(_gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer);
        renderTargetProperties.__webglDepthbuffer = _gl.createRenderbuffer();
        setupRenderBufferStorage(renderTargetProperties.__webglDepthbuffer, renderTarget, false);

      }

    }

    _gl.bindFramebuffer(_gl.FRAMEBUFFER, null);

  }

  // Set up GL resources for the render target
  function setupRenderTarget(renderTarget) {

    const renderTargetProperties = properties.get(renderTarget);
    const textureProperties = properties.get(renderTarget.texture);

    renderTarget.addEventListener('dispose', onRenderTargetDispose);

    textureProperties.__webglTexture = _gl.createTexture();

    info.memory.textures++;

    const isCube = (renderTarget.isWebGLCubeRenderTarget === true);
    const isMultisample = (renderTarget.isWebGLMultisampleRenderTarget === true);
    const supportsMips = isPowerOfTwo(renderTarget) || isWebGL2;

    // Handles WebGL2 RGBFormat fallback - #18858

    if (isWebGL2 && renderTarget.texture.format === RGBFormat && (renderTarget.texture.type === FloatType || renderTarget.texture.type === HalfFloatType)) {

      renderTarget.texture.format = RGBAFormat;

      console.warn('THREE.WebGLRenderer: Rendering to textures with RGB format is not supported. Using RGBA format instead.');

    }

    // Setup framebuffer

    if (isCube) {

      renderTargetProperties.__webglFramebuffer = [];

      for (let i = 0; i < 6; i++) {

        renderTargetProperties.__webglFramebuffer[i] = _gl.createFramebuffer();

      }

    } else {

      renderTargetProperties.__webglFramebuffer = _gl.createFramebuffer();

      if (isMultisample) {

        if (isWebGL2) {

          renderTargetProperties.__webglMultisampledFramebuffer = _gl.createFramebuffer();
          renderTargetProperties.__webglColorRenderbuffer = _gl.createRenderbuffer();

          _gl.bindRenderbuffer(_gl.RENDERBUFFER, renderTargetProperties.__webglColorRenderbuffer);

          const glFormat = utils.convert(renderTarget.texture.format);
          const glType = utils.convert(renderTarget.texture.type);
          const glInternalFormat = getInternalFormat(renderTarget.texture.internalFormat, glFormat, glType);
          const samples = getRenderTargetSamples(renderTarget);
          _gl.renderbufferStorageMultisample(_gl.RENDERBUFFER, samples, glInternalFormat, renderTarget.width, renderTarget.height);

          _gl.bindFramebuffer(_gl.FRAMEBUFFER, renderTargetProperties.__webglMultisampledFramebuffer);
          _gl.framebufferRenderbuffer(_gl.FRAMEBUFFER, _gl.COLOR_ATTACHMENT0, _gl.RENDERBUFFER, renderTargetProperties.__webglColorRenderbuffer);
          _gl.bindRenderbuffer(_gl.RENDERBUFFER, null);

          if (renderTarget.depthBuffer) {

            renderTargetProperties.__webglDepthRenderbuffer = _gl.createRenderbuffer();
            setupRenderBufferStorage(renderTargetProperties.__webglDepthRenderbuffer, renderTarget, true);

          }

          _gl.bindFramebuffer(_gl.FRAMEBUFFER, null);


        } else {

          console.warn('THREE.WebGLRenderer: WebGLMultisampleRenderTarget can only be used with WebGL2.');

        }

      }

    }

    // Setup color buffer

    if (isCube) {

      state.bindTexture(_gl.TEXTURE_CUBE_MAP, textureProperties.__webglTexture);
      setTextureParameters(_gl.TEXTURE_CUBE_MAP, renderTarget.texture, supportsMips);

      for (let i = 0; i < 6; i++) {

        setupFrameBufferTexture(renderTargetProperties.__webglFramebuffer[i], renderTarget, _gl.COLOR_ATTACHMENT0, _gl.TEXTURE_CUBE_MAP_POSITIVE_X + i);

      }

      if (textureNeedsGenerateMipmaps(renderTarget.texture, supportsMips)) {

        generateMipmap(_gl.TEXTURE_CUBE_MAP, renderTarget.texture, renderTarget.width, renderTarget.height);

      }

      state.bindTexture(_gl.TEXTURE_CUBE_MAP, null);

    } else {

      state.bindTexture(_gl.TEXTURE_2D, textureProperties.__webglTexture);
      setTextureParameters(_gl.TEXTURE_2D, renderTarget.texture, supportsMips);
      setupFrameBufferTexture(renderTargetProperties.__webglFramebuffer, renderTarget, _gl.COLOR_ATTACHMENT0, _gl.TEXTURE_2D);

      if (textureNeedsGenerateMipmaps(renderTarget.texture, supportsMips)) {

        generateMipmap(_gl.TEXTURE_2D, renderTarget.texture, renderTarget.width, renderTarget.height);

      }

      state.bindTexture(_gl.TEXTURE_2D, null);

    }

    // Setup depth and stencil buffers

    if (renderTarget.depthBuffer) {

      setupDepthRenderbuffer(renderTarget);

    }

  }

  function updateRenderTargetMipmap(renderTarget) {

    const texture = renderTarget.texture;
    const supportsMips = isPowerOfTwo(renderTarget) || isWebGL2;

    if (textureNeedsGenerateMipmaps(texture, supportsMips)) {

      const target = renderTarget.isWebGLCubeRenderTarget ? _gl.TEXTURE_CUBE_MAP : _gl.TEXTURE_2D;
      const webglTexture = properties.get(texture).__webglTexture;

      state.bindTexture(target, webglTexture);
      generateMipmap(target, texture, renderTarget.width, renderTarget.height);
      state.bindTexture(target, null);

    }

  }

  function updateMultisampleRenderTarget(renderTarget) {

    if (renderTarget.isWebGLMultisampleRenderTarget) {

      if (isWebGL2) {

        const renderTargetProperties = properties.get(renderTarget);

        _gl.bindFramebuffer(_gl.READ_FRAMEBUFFER, renderTargetProperties.__webglMultisampledFramebuffer);
        _gl.bindFramebuffer(_gl.DRAW_FRAMEBUFFER, renderTargetProperties.__webglFramebuffer);

        const width = renderTarget.width;
        const height = renderTarget.height;
        let mask = _gl.COLOR_BUFFER_BIT;

        if (renderTarget.depthBuffer) mask |= _gl.DEPTH_BUFFER_BIT;
        if (renderTarget.stencilBuffer) mask |= _gl.STENCIL_BUFFER_BIT;

        _gl.blitFramebuffer(0, 0, width, height, 0, 0, width, height, mask, _gl.NEAREST);

        _gl.bindFramebuffer(_gl.FRAMEBUFFER, renderTargetProperties.__webglMultisampledFramebuffer); // see #18905

      } else {

        console.warn('THREE.WebGLRenderer: WebGLMultisampleRenderTarget can only be used with WebGL2.');

      }

    }

  }

  function getRenderTargetSamples(renderTarget) {

    return (isWebGL2 && renderTarget.isWebGLMultisampleRenderTarget) ?
      Math.min(maxSamples, renderTarget.samples) : 0;

  }

  function updateVideoTexture(texture) {

    const frame = info.render.frame;

    // Check the last frame we updated the VideoTexture

    if (_videoTextures.get(texture) !== frame) {

      _videoTextures.set(texture, frame);
      texture.update();

    }

  }

  // backwards compatibility

  let warnedTexture2D = false;
  let warnedTextureCube = false;

  function safeSetTexture2D(texture, slot) {

    if (texture && texture.isWebGLRenderTarget) {

      if (warnedTexture2D === false) {

        console.warn("THREE.WebGLTextures.safeSetTexture2D: don't use render targets as textures. Use their .texture property instead.");
        warnedTexture2D = true;

      }

      texture = texture.texture;

    }

    setTexture2D(texture, slot);

  }

  function safeSetTextureCube(texture, slot) {

    if (texture && texture.isWebGLCubeRenderTarget) {

      if (warnedTextureCube === false) {

        console.warn("THREE.WebGLTextures.safeSetTextureCube: don't use cube render targets as textures. Use their .texture property instead.");
        warnedTextureCube = true;

      }

      texture = texture.texture;

    }

    // currently relying on the fact that WebGLCubeRenderTarget.texture is a Texture and NOT a CubeTexture
    // TODO: unify these code paths
    if ((texture && texture.isCubeTexture) ||
      (Array.isArray(texture.image) && texture.image.length === 6)) {

      // CompressedTexture can have Array in image :/

      // this function alone should take care of cube textures
      setTextureCube(texture, slot);

    } else {

      // assumed: texture property of THREE.WebGLCubeRenderTarget
      setTextureCubeDynamic(texture, slot);

    }

  }

  //

  this.allocateTextureUnit = allocateTextureUnit;
  this.resetTextureUnits = resetTextureUnits;

  this.setTexture2D = setTexture2D;
  this.setTexture2DArray = setTexture2DArray;
  this.setTexture3D = setTexture3D;
  this.setTextureCube = setTextureCube;
  this.setTextureCubeDynamic = setTextureCubeDynamic;
  this.setupRenderTarget = setupRenderTarget;
  this.updateRenderTargetMipmap = updateRenderTargetMipmap;
  this.updateMultisampleRenderTarget = updateMultisampleRenderTarget;

  this.safeSetTexture2D = safeSetTexture2D;
  this.safeSetTextureCube = safeSetTextureCube;

}

export {WebGLTextures};
